The invention relates to stent delivery systems, which are used to implant a stent into a patient""s body lumen to maintain the patency thereof. The stent delivery system is useful in the treatment and repair of body lumens, including coronary arteries, renal arteries, carotid arteries, and other body lumens.
Stents are generally cylindrically-shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other body lumen. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway therethrough. Stents also are useful in maintaining the patency of a body lumen, such as a coronary artery, after a percutaneous transluminal coronary angioplasty (PTCA) procedure or an atherectomy procedure to open a stenosed area of the artery.
Typically, a stent is delivered intraluminally through a percutaneous incision through the femoral or renal arteries. The stent is mounted on the distal end of an elongated catheter and the catheter and stent are advanced intraluminally to the site where the stent is to be implanted. A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally. Three different approaches for expanding stents have been developed in the art, namely, balloon expanded stents, elastically self-expanding stents, and heat expanded stents. Balloon expanded stents are placed over a deflated balloon mounted on the catheter. The balloon is then inflated to expand the stent radially outwardly into contact with the arterial wall, whereupon the stent undergoes plastic deformation and remains in an expanded state to hold open and support the artery. Elastically self-expanding stents are adapted to be delivered in an elastically compressed state while confined within an outer restraining sheath, but to elastically expand when the sheath is removed and to provide support to the vessel within which it is implanted. Heat expanded stents are made from heat-sensitive materials such as nickel-titanium, are cooled in a compressed shape before insertion into the patient, but assume a pre-existing expanded shape when exposed to the body temperature of a patient.
With respect to self-expanding stents, typically a retractable sheath is positioned over the self-expanding stent which is mounted on the distal end of the catheter. Once the catheter has been advanced intraluminally to the site where the stent is to be implanted, the sheath is withdrawn thereby allowing the self-expanding stent to expand radially outwardly into contact with the arterial wall, thereby holding open and supporting the artery. Both balloon expanded stents and heat sensitive self-expanding stents may also be delivered within a retractable sheath, similar to that used with a self-expanding stent. In such cases the sheath may function to secure the stent on the catheter during insertion or to prevent sharp edges of the stent from tearing at the wall of the lumen during insertion.
One embodiment of a catheter delivery system is the so-called xe2x80x9cover-the-wirexe2x80x9d delivery system, in which a catheter is introduced into the patient over a guide wire which has been previously introduced. In this embodiment, the guide wire runs within a lumen extending the entire length of the catheter. Another embodiment of the catheter delivery system is the so-called xe2x80x9crapid exchangexe2x80x9d delivery system, in which the guide wire runs within a lumen in the catheter extending from the distal tip of the catheter to a point just proximal of where the stent is positioned on the catheter, at which point the lumen terminates on the outside of the catheter and the guide wire emerges from the catheter to extend proximally, outside of the catheter. Thus, the catheter of a xe2x80x9crapid exchangexe2x80x9d delivery system has a guide wire lumen port at the distal end of the catheter, and a proximal port spaced a relatively short distance from the distal end and a relatively long distance from the proximal end of the catheter. This xe2x80x9crapid exchangexe2x80x9d configuration allows the surgeon to rapidly and single-handedly place the delivery system over the guide wire or to exchange one delivery system for another, because the length of the guide wire lumen in the catheter is much shorter than used in an over-the-wire delivery system.
One of the problems associated with the prior art catheter-delivery systems which use a retractable outer sheath is that the addition of a retractable sheath tends to reduce the overall flexibility of the delivery system. Another problem is that, in the case of the rapid exchange delivery system, the addition of a retractable sheath to surround the catheter introduces a problem of rotational alignment between the sheath and the catheter. Upon commencement of installing the delivery system over the guide wire, the surgeon must introduce the proximal tip of the guide wire into the catheter lumen at the distal tip of the catheter. The surgeon then advances the guide wire proximally through the catheter lumen until the proximal tip of the guide wire emerges from the catheter and protrudes through an opening in the wall of the sheath. If, during the foregoing process, the sheath rotates relative to the catheter, the surgeon may have difficulty in aligning the opening with the guide wire tip, so as to get the guide wire tip to protrude from the opening. This complication can be a major problem for the surgeon to resolve under the pressure of surgery.
Thus, there has been found in the art a need for a reliable rapid-exchange stent delivery system for a self expanding stent, in which rotational alignment between the outer sheath and the catheter may be maintained prior to and during the process of positioning the delivery system over the guide wire. Further, the art has found a need for a delivery system for a self expanding stent which has improved flexibility characteristics. The present invention addresses these and other needs.
The present invention is directed to a catheter delivery system having improved flexibility characteristics. In a further aspect, the invention is directed to a rapid-exchange catheter delivery system having an outer sheath, in which the sheath is held in rotational alignment with the catheter prior to and during the process of positioning the delivery system over a guide wire. Means for maintaining such rotational alignment may assume the form of a leaf-spring or other expanding member attached to the catheter and adapted to protrude through a slot or opening defined in the sheath.
A catheter assembly for removably attaching an intravascular stent is provided in which an elongated catheter has an inner member and an outer member extending along a longitudinal axis wherein the inner member and the outer member have a coaxial configuration and are dimensioned for relative axial movement. A self-expanding stent, having an open lattice structure, and being adapted to be expandable to an open configuration, is mounted on the inner member, within the outer member.
The present invention includes a leaf spring, attached to the inner member, which engages with a slot on the outer member so as to maintain the inner member and the outer member in rotational alignment. The leaf spring is adapted to deflect radially inwardly and to disengage from the slot in the outer member, either after the distal tip of a guide wire is extended from within the outer member over the leaf-spring outwardly through the slot in the outer member, or when the outer member is proximally withdrawn relative to the inner member.
In a further aspect of the invention, the distal end of the inner member is configured as a helical coil to enhance the overall flexibility of the delivery assembly.
The invention also includes a method of implanting a self-expanding stent utilizing the catheter-delivery system described above. Using the catheter-delivery system, a guide wire is proximally advanced through a lumen of the delivery system from the distal end until it encounters the leaf-spring, whereupon the guide wire is deflected outwards through the slot. The leaf spring is deflected radially inwardly and disengages from the slot in the outer member when the outer member is proximally withdrawn relative to the inner member.
The invention also relates to a method of assembling the delivery system described above. The method includes inserting the ends of the leaf spring through the wall of a tubular sleeve so that the ends are positioned within the lumen and the center portion of the leaf-spring is positioned outside the lumen of the sleeve. The sleeve is then slid over the inner member to a desired position on the inner member. The sleeve may be attached by friction fit, adhesive, or laser welding.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings.